RU1838755C - Angular displacement differential capacitive converter - Google Patents

Abstract

 HOI an The invention relates to measuring equipment and is intended to expand the dyson of the measured angular displacement to 360 and increase accuracy by reducing the influence of the skew of the electrodes of the differential capacitive angular displacement transducer, which contains two fixed electrodes formed by four rings lying in a common plane and separated by insulating spirals into sections interconnected in a certain way, the current radii of the spirals are interconnected by specified mathematical relations wear it. A movable electrode mounted rotatably in a parallel plane consists of annular sectors arranged diametrically opposite in the common plane and forming two capacitors of variable capacitance with differentially variable capacities with stationary electrodes. Protective ring electrodes are also available. The measuring circuit to which the transducer electrodes are connected implements a ratiometric measurement method. 1 C.p. f-ls, 1 ill. SL

Description

The invention relates to measuring technique and can be used to measure the angular displacements of various objects in instrumentation or automation.

The aim of the invention is to expand the range of the measured angular movement to 360 ° and to increase the accuracy of reducing the effect of skewing of the electrodes.

The drawing shows in one plane the fixed and movable electrodes of a capacitive transducer and their connection to the measuring unit.

The differential capacitive angular displacement transducer comprises two stationary electrodes placed in the same plane and formed by four concentric rings 1-4 of different diameters. The area of each of the rings is divided into two electrically isolated parts using spirals 5-8, while all spirals increase in one direction. The beginnings of the spirals of the first and fourth rings are located on the same line passing through the axis of rotation of the third electrode, which coincides with the geometric center of the rings. The beginning of the spirals of the second and third rings are on this

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the same line from the opposite side from the center.

The first fixed electrode is formed by electrically interconnected sections of rings 1 and 2, bounded by their inner ring sides with radii RO and RI and the spirals 5 and 6 separating these rings, and also sections of rings 3 and 4 bounded by spirals 7 and 8 and the outer sides of these rings with radii RS and R4. The second fixed electrode is formed by the remaining electrically connected sections of the four rings.

In parallel with two stationary electrodes, a third electrode 9 is mounted rotatably. These electrodes form a differential capacitor with capacitances Ci and C2 varying as a function of the angular position of the third; electrode. . . :. :; - .; .: ;; ..: ..... - ..,

The third electrode 9 consists of two conductive ring sectors 10 and 11 located opposite the rings 1 and 4, fixed electrodes and a third conductive ring sector 12 located diametrically opposite to the first two and opposite the rings 2 and 3 of the fixed electrodes.

The angular value a of the sectors of the electrode 9 (Fig. 1} can be chosen arbitrarily, it should be borne in mind that for a small value a the absolute capacity of the converter is small, on the other hand, an increase in a leads to a decrease in the range of measured angles equal to (360 ° - and).;

The current radii of the spirals are determined from the condition of compensating the distortions of the electrodes and the required dependence of the resulting capacitance of the transducer C from the angle of rotation of the movable electrode 9 relative to the stationary electrodes. The values of the current radii of n spirals are obtained by expanding in the Taylor series the resulting capacitance of the transducer and equating to zero the linear and quadratic terms of the expansion. The last equation for finding n is obtained by choosing the desired dependence of the resulting capacitance C on the angle of rotation p of the electrode 9 and expressing this dependence. through the current radii of n spirals. In the preparation of the equations, a small radial distance between the rings of the stationary electrodes is taken into account, which is necessary for their isolation from each other.

In the case when the dielectric constant Ј of the converter is constant during its operation, the measuring unit 13 is an output device

the voltage of which is directly proportional to the resulting capacitance C Ci-C2. If the dielectric constant k varies significantly during operation,

the converter is equipped with an additional constant capacitor with a capacitance C3, the dielectric constant of which depends on the parameters of the external environment in the same way as the resulting capacitance of the converter. The measuring unit 13 comprises in this case an additional division unit. The output voltage of the measuring unit is then proportional to f

only relationship

It is advisable to use the total capacity of Sch + € 2 as the capacitance Cz. However, this capacitance largely depends on the skew angle between the electrodes, since its expansion in the Taylor series includes a non-zero quadratic

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For To eliminate this drawback, the converter is equipped with two additional ring electrodes 14 and 15, which are located in the same plane as the stationary electrodes, as well as two additional ring sectors 16 and 17, which are located in the same plane as the movable electrode 9. The electrodes 14 and 15 are electrically connected interconnected, connected to the measuring unit 13 and arranged concentrically with two stationary electrodes, covering them

outside.

The annular sectors 16 and 17 are located opposite the rings 14 and 15, respectively, while being diametrically opposed to each other, as well as electrically connected

with a movable electrode 9. The ring sectors 16 and 17 form with the ring electrodes 14 and 15 two parallel capacitors with a total capacity of GI. The geometric dimensions of the electrodes 14 and 15 and sectors 16 and 17 are selected so that in the expansion in the Taylor series C4 along the angle of the skew of the electrodes, the linear term of decomposition is equal to 0, and the quadratic term of decomposition is equal to

to the similar expansion term Ci + € 2- In case the ring sectors 16 and 17 are located in a line with the sectors along. movable electrode 9, capacitance Cz Ci + C - C4 is independent of the bias of the electrodes with

5 accurate to the quadratic term of the expansion. If the ring sectors 16 and 17 are perpendicular to the sectors of the movable electrode 9, the capacitance C3 Ci + C2 + C3 also does not depend on the skew

electrodes up to quadratic decomposition.

In the event that the spirals 5, 6, 7, 8, which form the stationary electrodes, have a significant thickness and the condition Ci + C2 const is violated, the ring electrodes til and 15 need to be slightly profiled from the condition C3 const, If the metallization of the stationary electrodes HiJ is applied on their inner surface, then in the rings of the electrodes 14 and 15 it is necessary to make narrow cuts for the conclusions of the stationary electrodes outside the converter. G hey metallization of stationary electrodes on the outer surface to do this; z is required. The measuring unit 13 in the presence of the capacitor C4 contains an additional summing unit, and its output is the voltage in direct proportion to the following ratio: C | -C2

Sz; ..

The device operates as follows. With the angular movement of the movable electrode 9 relative to the stationary electrodes, the overlap area between them changes, therefore, the converter capacitance changes. In the event of a skew occurring between the movable and fixed electrodes, the capacitances Ci and C2 change in the same way. Consequently, the resulting capacitance Ci-C3 will not depend on the skewness of the electrodes.

This converter allows reducing the error introduced by the distortions of the electrodes by 3-5 times or, with the initial error, reducing the dimensions of the device accordingly.

Claims (2)

1. A differential capacitive angular displacement transducer containing two fixed, electrically (isolated) electrodes that are made in the form of concentric rings located in the same plane, mounted coaxially with the possibility of rotation in the parallel plane of the electrode, made E form conductive, electrically interconnected annular sectors, e k insulated on a common dielectric base and located on both sides and relative to the axis of rotation of this electrode, and connected to these Electrode measuring unit, characterized in that, in order to expand the range of v zmer emogo angular movement up to 360 ° vi improve accuracy by reducing skew ELIYANIYA electrodes, it is provided with the third and fourth fixed rings installed concentrically with the first two in a common plane with them, the area of each of the four rings is divided into two parts by an insulating spiral, the beginning of each of which is located on the inner side of the corresponding ring, the current radii of all the spirals increase in the same angular direction, the beginning of the spirals on the first and fourth rings, respectively having the smallest and largest diameters, are located on the same line passing through the geometric center of the rings along storo5 well bottom from the axis of rotation, and spirals beginning at the second and third rings disposed between said, it is arranged diametrically opposite with respect to the respective coils at the first and In the fourth rings, one of the fixed electrodes is formed by electrically connected sections of the first and second rings bounded by their inner ring sides and by spirals separating these rings, as well as sections of the third and fourth rings bounded by the corresponding spirals and the outer sides of these rings the second fixed electrode is formed 0 remaining electrically connected. sections of four rings, two conductive annular sectors of the third electrode are different. placed opposite the first and fourth rings of fixed electrodes, and 5, the third ring sector of this electrode located diametrically opposed to them is placed opposite the second and third rings of fixed electrodes, and the current values of the radii of the whiskers and spirals, where i is the serial number of the spiral (I, II, III, IV), are related by the following relations : Ai and A nv + pi - rp - ri const, riv3 - rsh3 const, 5 ru3- P3 const, 2. Transmitter of Clause 1, with the exception of JO- and that it is equipped with two additional fixed annular rings connected to the measuring unit 0 electrodes that are electrically connected to each other are located concentrically in the same plane with two fixed electrodes and cover them from the outside, as well as two additional 5 ring sectors, which are located in the same plane as the ring sectors of the third electrode, are electrically connected to it, located opposite the respective additional rings and diametrically opposite one to the other, and their radii RK, where k 5,6,7,8, are related by the following ratios: Re4 - + Re4 - Rs - const, Re3 - - Re3 + Rs3 O, where Rs and R are internal, and Re and Re are external radii of additional rings and additional 5 ring sectors. L B fj